1. Technical Field
The present invention relates to an input device and a display device with an input function equipped with the input device.
2. Related Art
In recent years, there has been provided an electronic apparatus, such as a cellular phone, a car navigation, a personal computer, a ticket-vending machine, or a bank terminal, in which an input device is disposed on the face of an image forming device of the apparatus, where it is possible to input information with reference to an image displayed in the image forming device. In such an input device, as shown in FIG. 8, a resistive film type touch panel is configured with a first light-transmissive insulating substrate 10 and a second light-transmissive insulating substrate 20 which are disposed to face each other leaving a predetermined gap interposed therebetween, and light-transmissive resistive films 11 and 21 are formed on the surfaces of the substrates which face each other. When a liquid crystal device 5 is used as the image forming device, it is equipped with a liquid crystal panel 5a in which liquid crystal is disposed between a pair of substrates 50x and 60x, and an upper polarizing plate 81 (the upper polarizing plate of the image forming device) is disposed so as to overlap on the side of the liquid crystal panel 5a on which the touch panel 2 is disposed. When the liquid crystal panel 5a is a light-transmissive liquid crystal panel or a semi-transmissive reflective liquid crystal panel, a lower polarizing plate 82 and a backlighting device (not shown) are disposed on the opposite side of the liquid crystal panel 5a to which the touch panel 2 is disposed.
Herein, light is reflected from the interface of materials and the reflection degree increases when light enters a material with a higher refractive index through a material with a lower refractive index. Therefore, when outside light enters the touch panel 2, a high degree of reflection of light occurs from the surface of the resistive film 11 formed on the surface of the first insulating substrate 10. As a result, there may be problems in that the quality of image displayed on the liquid crystal device 5 deteriorates.
Therefore, it has been suggested to configure the input device by disposing a first ¼ wavelength plate 91x between the upper polarizing plate 81 and the touch panel 2, and by disposing a polarizing plate 93x for reflection prevention to overlap with a second ¼ wavelength plate 92x on the surface for the input operation on the touch panel 2. In such configuration, the retardation axis of the first ¼ wavelength plate 91x, the retardation axis of the second ¼ wavelength plate 92x, and the absorption axis of the polarizing plate 93x on the touch panel side respectively have angles in relation to the absorption axis of the upper polarizing plate 81 of 45°, 45°, and 0°. The retardation axis of the first ¼ wavelength plate 91x and the retardation axis of the second ¼ wavelength plate 92x are disposed to be at right angles to each other (refer to Japanese Patent No. 3854392 and JP-A-10-48625).
According to such configuration, among the outside light, linearly-polarized light transmitted from the polarizing plate 93x on the touch panel side travels through the second ¼ wavelength plate 92x to be circularly-polarized light and arrives at the touch panel 2. The light reflected from the touch panel 2 becomes inversely rotating circularly-polarized light. The light which travels through the second ¼ wavelength plate 92x is changed into linearly-polarized light in a direction perpendicular to the incident linearly-polarized light, and is not emitted to the outside from the polarizing plate 93x on the touch panel side. Moreover, since the retardation axes of the first ¼ wavelength plate 91x and the second ¼ wavelength plate 92x are disposed to be at right angles to each other, their optical properties cancel each other out. Therefore, display light transmitted from the upper polarizing plate 81 arrives at the polarizing plate 93x on the touch panel side as linearly-polarized light without having changed and the light is emitted.
However, in the case where a device is configured as shown in FIG. 8, it is necessary to dispose the retardation axes of the first ¼ wavelength plate 91x and the second ¼ wavelength plate 92x to be at right angles to each other. Therefore, the retardation axis of the first ¼ wavelength plate 91x, the retardation axis of the second ¼ wavelength plate 92x, and the absorption axis of the polarizing plate 93x on the touch panel side respectively have angles in relation to the absorption axis of the upper polarizing plate 81 that must be set to 45°, 45°, and 0°. For that reason, when the alignment of the absorption axis of the upper polarizing plate 81 is set, the directions of the retardation axes of the first ¼ wavelength plate 91x and the second ¼ wavelength plate 92x and the direction of the absorption axis of the polarizing plate 93x on the touch panel side must also be set. As a result, there are problems in that it is difficult to freely design the device. In the case of constructing, for example, a display device with an input function which is usable while wearing sunglasses having a polarizing property according to the configuration shown in FIG. 8, it is necessary to change the rubbing direction and the direction of the absorption axis of the upper polarizing plate 81 in the rubbing process during the manufacture of the liquid crystal panel 5a. As a result, there are problems in that it is difficult to standardize and decrease the price.